For reeling a continuous paper web from a paper machine to a paper reel, reel-ups have been used hitherto which are generally designed having two systems to enable continuous production to be maintained, namely a primary system which takes over an empty reeling drum from a pair of lowering arms and, when the paper web has been wound a few turns on the drum, a secondary system where reeling is continued to a finished reel of paper. In the present context we have chosen to use the adjective "secondary" in the terms "secondary system", "secondary unit", "secondary member", "secondary body", etc., even if the reel-up does not have a primary system. The secondary system usually comprises either a pair of secondary arms or a pair of secondary carriages which are pivoted or displaced linearly depending on the increase in diameter of the paper reel.
In reel-ups of the first type, i.e., with secondary arms, the reeling occurs, briefly, as follows: An empty reeling drum is transferred from a stock of drums to primary forks which bring it into contact with a driven surface winding drum over which the web runs, in order to initiate reeling of the web. Considerable friction thus occurs between the reeling drum and the surface winding drum, so that the reeling drum is generally caused to rotate at the same speed as the surface winding drum before coming into contact with this. The reeling drum is then moved along the periphery of the surface winding drum, down to two parallel, horizontal stand members where the secondary arms take over control of the reeling drum. Continued reeling to a finished reel is achieved in that the secondary arms, turning around a joint, follow the reel along its horizontal movement while press devices in the form of rotating, journalled press rolls, arranged on the secondary arms, act against bearing houses arranged on the end portions of the reeling drum. A desired, controllable linear pressure is thus maintained in the nip between the surface winding drum and the paper reel as it increases in size. However, the pivoting movement of the secondary arms causes the linear pressure to be uneven since the press reels press against the reeling drum in a contact point following the envelope surface of the bearing house in an arc-shaped movement, giving both a horizontal and a vertical movement component. Reel-ups with secondary arms are described in the following patent specifications, for instance: U.S. Pat. No. 4,143,828, U.S. Pat. No. 4,283,023, U.S. Pat. No. 4,175,714, U.S. Pat. No. 3,614,011 and U.S. Pat. No. 5,520,354.
Another deficiency in reel-ups with secondary arms is that the diameter of the finished paper reel is limited to the span of the secondary arms and if a large paper reel is required, secondary systems consisting of linearly movable secondary carriages provided with press devices must be used instead. The problem of the uneven linear pressure caused by the pivoting movement of the secondary arms is then also solved since the press devices on the carriages only have a horizontal movement component during movement of the reeling drum in relation to the surface winding drum. It is also less complicated to measure the growth of the reel with the aid of the horizontal movement of the carriage than with an angle transducer on a secondary arm. Reel-ups with linearly movable secondary carriages are described in the following patent specifications, for instance: U.S. Pat. No. 4,934,619 and U.S. Pat. No. 5,370,327.
With increasing reeling velocities and increasing size of the paper reel, however, slipping may occur between the surface winding drum and paper reel. Furthermore, the individual layers in the reel may be wound too loosely, particularly in the manufacture of soft paper such as "soft tissue" and similar paper used for sanitary purposes, since the linear pressure in the nip must be low to avoid negative effects in the paper reel, which may cause slipping between adjacent layers, causing them to be displaced axially along the paper layers below. These problems are solved by equipping the secondary system with central driving of the reeling drum. Central driving means that the reeling drum is connected to a drive means with the aid of a coupling device disposed at the ends of the reeling drum. Central driving also enables variation of the linear pressure within a wide area so that compression of the paper web in the nip between paper reel and surface winding drum can be reduced. Reel-ups with central driving are described in the following patent specifications, for instance: U.S. Pat. No. 4,934,619, U.S. Pat. No. 5,370,327, U.S. Pat. No. 5,520,354, U.S. Pat. No. 5,375,790 (SE-469 071) and U.S. Pat. No. 5,393,008 (SE-469 072).
In order to maintain the desired high stretchability in the tissue paper, an endless belt may be used as support means, either on its own or together with a surface winding drum. The endless belt also alleviates other control problems in the form of vibrations or the like in the web prior to the surface winding drum. Reel-ups with endless belts are described in the following patent specifications, for instance: U.S. Pat. No. 4,143,828, U.S. Pat. No. 4,283,023, U.S. Pat. No. 5,531,396 and U.S. Pat. No. 4,175,714.
With the use of central driving, a changeover must be effected between the different drive arrangements at the transfer of the reeling drum from the primary system to the secondary system, which affects the linear pressure negatively since a temporary pressure increase occurs in the nip. To optimize reeling, therefore, the same drive means should be connected throughout the reeling procedure from the start, with an empty reeling drum, to a finished reel so that the variation in tension otherwise occurring in the paper web can be eliminated. To achieve this it is already known to use double sets of secondary carriages only which alternate with each other and enable omission of the primary arms altogether. In this way a single drive means connected to one of the carriage pairs can follow the reeling drum throughout the reeling process to a finished reel. A reel-up of this type is described in U.S. Pat. No. 5,370,327. However, a special stand is required for the reel-up described therein to enable the carriage pairs to pass each other; i.e., the stand is provided with two pairs of parallel rails, pivotably journalled in the downstream end of the stand. The surface winding drum has also been arranged vertically movable. This means that the existing reel-ups cannot be directly equipped with double secondary units, nor can they easily be converted to reel-ups with double secondary units.
Furthermore, drive arrangements for central driving according to U.S. Pat. No. 5,370,327 have been arranged on each side of the stand, on separate support elements. The drive arrangements and each secondary unit have separate actuators for the to and fro movement along the separate support elements. The drive arrangement is also disconnected before the reeling drum has been grasped by the secondary unit. This creates difficulties when aligning and coupling together the reeling drum with the central driving during operation. As will be understood, the stand and support elements, arranged beside each other, also require a considerable amount of space.
When the reeling drum runs along the stand rails during production of a new paper reel there is risk of foreign bodies, e.g., collected dust from the paper web, preventing or obstructing the horizontal movement. A common problem associated with the above-mentioned reel-ups is therefore the difficulty in gaining easy access to the internal parts of the reel-up for repair, service and cleaning.
Finally, another major problem common to all known reel-ups, both with and without primary systems, is undesired friction forces which complicate control of the linear pressure in the nip between drum and the growing paper reel. In a reel-up with a linear loading system comprising horizontally movable secondary units for the reeling drum, it is the friction between reeling drum and stand rails, the stand-rail friction, that causes the greatest limitation of accuracy and reliability in controlling the linear pressure in the roll nip.